1. Field of the Invention
The present invention relates to a production process for an oxide magnetic material capable of being used in a stacked composite device and an inductor and to the oxide magnetic material.
2. Related Art
In recent years, a demand for downsizing has been increasingly built up in a small-sized electronic device such as a portable telephone. In such a situation, plural electronic circuits constituting an electronic device have been integrated into a stacked composite device on a single chip for mounting on a main substrate.
FIG. 7 is a perspective view showing an example of stacked composite device and FIG. 8 is an exploded perspective view thereof. A stacked composite device, as shown in FIGS. 7 and 8, is constructed by stacking plural ceramic layers 3 and 4. Plural circuit element patterns 11 each including an inductor or a capacitor are formed on surfaces of the ceramic layers 3 and 4. The circuit element patterns 11 are connected to each other by via holes 12 passing through the ceramic layers 3 and 4 or by conductor patterns formed on the ceramic layers 3 and 4, thereby to construct an electronic circuit such as a filter.
It is proposed that in a case where the ceramic layers 3 are magnetic ceramic layers and the ceramic layers 4 are dielectric ceramic layers, a pattern (L pattern) constituting an inductor is formed on each of the magnetic ceramic layers 3 and a pattern (C pattern) constituting a capacitor is formed on each of the dielectric ceramic layers 4 (Japanese Patent Laid Open No. S60-106114, Japanese Patent Laid Open No. H6-333743 and others).
As magnetic materials used in such a stacked composite device and an inductor, there has been generally heretofore used: a NiCuZn base spinel type ferrite. FIG. 9 is a graph showing frequency characteristics of magnetic permeability of a NiCuZn base spinel type ferrite. In FIG. 9, there are shown normalized values of a real part μ′ and an imaginary part μ″ of a complex magnetic permeability with the μ′ at 10 MHz as 1. As shown in FIG. 9, the real part μ′ of a complex magnetic permeability takes a comparatively high value in a region up to as high as a value in the vicinity of 100 MHz.
As magnetic materials capable of adapting to higher frequencies, there can be named a hexagonal ferrite. The hexagonal ferrite includes crystal structures of phases which are analogous to each other, such as a Z type, a Y type, a W type and an M type. The phase of the Z type, among them, shows a comparatively high magnetic permeability and reduction in magnetic permeability is minimized in a region up to as high as the GHz band.
A prior art spinel ferrite such as that of NiCuZn base, as shown in FIG. 9, can be used in a region up to as high as 100 MHz, whereas a natural resonance occurs in a region of higher frequencies to decrease a real part μ′ of magnetic permeability but to contrary to this, increase an imaginary part μ″ thereof (which is a Snoek limit). Furthermore, in a prior art hexagonal ferrite having the Z type structure, reduction in magnetic permeability is minimized and excellent in a high-frequency characteristic in a region up to as high as the GHz band, whereas a crystallization temperature is as high as 1300° C. Since Ag and Cu as materials of a conductor pattern are molten at such a high temperature, a problem arises that the conductor pattern cannot be heated simultaneously with sintering of a magnetic material.